Abstract
Shipping is the backbone of global freight. However, due to its currently strong reliance on fossil fuels, it accounts for 3 % of global greenhouse gas emissions, highlighting both the need and challenge of achieving the required rapid decarbonization. Over the past decade, Onboard carbon capture and storage (OCCS) has gained interest as a potential mitigation strategy while alternative fuels continue to develop. However, several capture technologies could be considered to capture the resulting CO2. In order to identify the most promising ones, this study performs a screening of different capture technologies (including absorption, membrane-assisted liquefaction, adsorption-assisted liquefaction, calcium-looping) through the case of a combination carrier under retrofit and newbuilding scenarios.
Overall, the results indicate that retrofit installations can reduce CO2 emissions by at least 45 %, even when using the existing ship power system. Once the utility (heat and power) is assumed sufficient (newbuilding scenario), up to 90 % reduction rates become feasible. Although the additional fuel usage is not negligible in the retrofit and newbuilding scenarios, the net emission reduction remains substantial, making onboard CCS a viable decarbonization measure. Among the process options, the absorption system demonstrates high capture potential with various heat sources but faces deployment challenges due to tall columns and chemical handling. Electricity-driven capture (membrane- and adsorption-assisted liquefaction) offers simpler configurations with competitive energy demands, with membrane-assisted liquefaction appearing to be the most energy-efficient and compact. Calcium-looping, and its hybridization with MEA, is a potential alternative when accessible energy for OCCS is limited onboard and when the sorbent material costs are low.
Finally, it is important to note that several factors such as ship type, sailing distance, fuel costs, and regulations will impact the performance of OCCS. Therefore, a detailed design and cost analysis are likely necessary to understand the competitiveness of OCCS compared to alternative approaches to reduce emissions from ships.